1. Field of the Invention
The present invention relates to an optical pickup device and a method of fabricating the same.
2. Description of the Background Art
An optical pickup device used for an optical disk device or the like records information on and reads out the information from an optical recording medium such as an optical disk using laser light, or detects a servo signal. In recent years, an optical pickup device using a transmission type holographic optical element which is one type of diffraction element has been studied and developed with demands for miniaturization, light weight, and low cost thereof.
FIG. 45 is a schematic view showing an optical pickup device having a transmission type holographic optical element disclosed in Japanese Patent Laid-Open No.76035/1991. The optical pickup device performs tracking servo using a three-beam method.
In FIG. 45, a semiconductor laser chip 202 is mounted on a side surface of a stem 201, and a photodetector for signal detection 206 is mounted on the upper surface of the stem 201. A first holographic functional plate 203 and a second holographic functional plate 204 are disposed above the semiconductor laser chip 202.
The semiconductor laser chip 202 emits laser light upward. The laser light emitted from the semiconductor laser chip 202 is divided into three diffracted light beams by the first holographic functional plate 203, to pass through the second holographic functional plate 204. The three diffracted light beams passing through the second holographic functional plate 204 are gathered on a disk 200 by a lens 205, to form three spots. The laser light reflected by the disk 200 (returned light) is diffracted by the second holographic functional plate 204, and is received by the photodetector for signal detection 206.
Since in the optical pickup device shown in FIG. 45, the semiconductor laser chip 202 and the photodetector for signal detection 206 are arranged at right angles on the stem 201, the stem 201 must be rotated through 90.degree. in mounting the semiconductor laser chip 202 and the photodetector for signal detection 206 and performing wire bonding. Therefore, the fabrication steps become complicated.
The stem 201 having a three-dimensional shape is used, whereby it is difficult to thin the optical pickup device. Further, the semiconductor laser chip 202 and the photodetector for signal detection 206 must be arranged in such a manner that a focusing spot of the returned light from the disk 200 is incident on the photodetector for signal detection 206, whereby high precision is required in mounting the semiconductor laser chip 202 and the photodetector for signal detection 206. Since the semiconductor laser chip 202 and the photodetector for signal detection 206 are arranged in three dimensions, however, it is difficult to realize high mounting precision.
FIG. 46 is a cross-sectional view of an optical pickup device disclosed in Japanese Patent Laid-Open No. 313987/1989.
In FIG. 46, a laser chip 42, a light detecting element for monitoring 43, and a light detecting element for signal reading 44 are contained in a cap 45, and a holographic optical element 46 is mounted on the cap 45. Laser light emitted from the laser chip 42 is gathered on a disk 49 by a collimator lens 47 and an objective lens 48 upon passing through the holographic optical element 46, and returned light from the disk 49 is received by the light detecting element for signal reading 44 upon being diffracted by the holographic optical element 46.
In the optical pickup device, the holographic optical element 46 is so moved on the cap 45 that a focusing spot of the returned light is incident on the light detecting element for signal reading 44 before being fixed, so that the position of the holographic optical element 46 can be adjusted.
Since it is difficult to adjust the position in the height direction of the holographic optical element 46, however, it is not easy to gather the returned light on a light detecting surface of the light detecting element for signal reading 44 most suitably. Further, the cap 45 having a three-dimensional shape is used, whereby it is difficult to thin the optical pickup device.
Therefore, an optical pickup device in which a holographic optical element can be adjusted in a three-dimensional manner has been proposed in Japanese Patent Laid-Open No. 96393/1996. FIG. 47 is a cross-sectional view of a conventional optical pickup device disclosed in Japanese Patent Laid-Open No. 96393/1996.
In FIG. 47, a mount member 51 is constructed upon integrating a lead frame 52 and a plurality of leads (not shown) by an insulating molding member 54. The insulating molding member 54 is so provided with a recess 55 that the surfaces of the lead frame 52 and the leads are exposed, and an electrically conducting sub-mount (a heat sink) 56 is mounted on the lead frame 52 in the recess 55. A photodiode for monitoring 57 is formed on a part of the upper surface of the sub-mount 56.
Furthermore, a semiconductor laser device 58 is mounted on the sub-mount 56. Laser light is respectively emitted from a front facet and a rear facet of the semiconductor laser device 58, and the laser light emitted from the rear facet is received as monitoring light by the photodiode 57.
A reflection type three-beam generating diffraction grating 59 is arranged ahead of the semiconductor laser device 58. A diffraction grating surface 59a of the three-beam generating diffraction grating 59 divides the laser light emitted from the front facet of the semiconductor laser device 58 into 0th-order, +1st and -1st diffracted light beams, and reflects the diffracted light beams upward at right angles. A light detecting element for signal detection 60 is mounted on the lead frame 52 behind the three-beam generating diffraction grating 59.
A first member 63 having a cylindrical cavity, a cylindrical second member 64 having a cavity in its inner part, and a cylindrical third member 65 having a cavity in its inner part are combined with each other on the recess 55 of the insulating molding member 54. The second member 64 is slidably inserted in the circumferential direction and the vertical direction with respect to the first member 63. The third member 65 is fitted in the second member 64 slidably in the horizontal direction. A transmission type holographic optical element 62 is fixed to an upper end of the third member 65. The first member 63 is fixed on the mount member 51 with adhesives 70a, while the second member 64 and the third member 65 are fixed to the first member 63 with adhesives 70b after adjustment.
The laser light emitted from the front facet of the semiconductor laser device 58 is divided into 0th-order, +1st and -1st diffracted light beams by the three-beam generating diffraction grating 59, and the diffracted light beams are reflected toward the transmission type holographic optical element 62. The diffracted light beams are then reflected at approximately right angles by a mirror (not shown) after passing through the transmission type holographic optical element 62, and are further gathered on an optical recording medium by a condenser lens. Therefore, a main spot and two sub-spots are formed on the optical recording medium.
Returned light from the optical recording medium is incident on the transmission type holographic optical element 62 upon following the condenser lens and the mirror in this order. The returned light is received by the light detecting element for signal detection 60 upon passing through the transmission type holographic optical element 62 while being diffracted into 1st (or -1st) order light beams.
In the optical pickup device shown in FIG. 47, the second member 64 is slidable and rotatable in the vertical direction, and the third member 65 is slidable in the horizontal direction before the second member 64 and the third member 65 are fixed, whereby the transmission type holographic optical element 62 can be easily moved in a three-dimensional manner.
In the conventional optical pickup device shown in FIG. 47, however, laser light is emitted perpendicularly to the surface of the lead frame 52, and approximately ten leads which are required to take out electric wiring are arranged along the width of the lead frame 52, whereby it is difficult to thin the optical pickup device in a direction perpendicular to the direction in which the laser light is emitted.
Furthermore, a plurality of members are used for moving the transmission type holographic optical element 62 in a three-dimensional manner, whereby the construction of an adjusting system becomes complicated. Further, the transmission type holographic optical element 62 is arranged above the mount member 51 by the plurality of members, whereby it is unstable in terms of construction.